Many foods are sold in containers which require the removal of the lids thereof to prevent an explosion of their contents during a heating process. In some cases, it is necessary to strike holes into the lid of the container before heating the contents thereof. Still other arrangements supply a secondary lid which is used after the removal of a primary lid.
Various U.S. Patents are available which disclose structures for sealed packages especially useful in connection with microwave ovens and the like. These patents include U.S. Pat. Nos. 3,997,677; 4,141,487; 4,210,674; and 4,404,241.
In U.S. Pat. No. 3,997,677 Arthur Hirsh et al disclose a package capable of withstanding prolonged exposure to relatively high temperatures. The package is formed from a composite film which includes a thermostable, thermoplastic layer and a polyolefin layer having a relatively low softening point. The package is a hermetically sealed construction which includes a weakened seal area which acts as a pressure release valve and which may be employed as a serving dish as well as a heating container.
Clifford Faust et al disclose in U.S. Pat. No. 4,141,487 a disposable package having an upper layer composed of a thin film plastic material, having a sealed, pleated section extending from opposite parallel sides intermediate the ends thereof and an elongated vent disposed within the pleated section. The sealed, pleated section is adapted to open and expose a vent at a predetermined temperature below the cooking temperature of the product.
In U.S. Pat. No. 4,210,674, Richard Mitchell discloses a paperboard tray covered by a plastic film bonded to upper edges of the tray sidewalls. The film provides a barrier against contamination of the food therein. The film and tray are transparent to micro-wave energy for heating the food and automatic venting of the covered tray while heating is afforded by a relatively small strip of electrically conductive material on the film. This material is absorptive of micro-wave energy in an amount sufficient to melt a vent opening in the film.
In U.S. Pat. No. 4,404,241, Robert Mueller et al disclose a multilayered heat material and a package involving the use of the same. The materials have apertures sealed with an extrudable hot melt material which conveys moisture barrier properties and is adapted to soften and permit venting of vapor generated in the package prior to distortion of the seam. The Mueller construction depends upon an extremely low sealing melt to soften and blow open heated vent opening. The material itself seals the associated hole and therefore possesses barrier properties.